Friday, November 18, 2016

Historically Does US Warmth In Fall Connect to Higher Eurasian Snow Cover?

The snow cover across northern Asia is now 3rd highest since record keeping began in the mid 1960s for early November.

The northern Pacific jet has been very strong and stable with little "waviness" until the last few days. The low over the Aleutian Islands is locked in place as the strong northern Pacific jet undercuts the low pumping up the ridge across North America locking in abnormally warm temperatures.

November temperatures vs normal

Is the high snow cover across Asia influencing the strong jet stream? Is there a history of this in early November in very high/very low Eurasian snow cover years?

While this year's cool pool in the northern Pacific has expanded recently, three of the top four years had significantly larger and colder cool pools (reanalysis is in Kelvin). Interestingly, widespread US warmth from mid October to mid November only occurred in 2016, 2015, 2014, 2012 and 2009.

1976

1972

2016

1969

2015

2012

1973

2009

2014

1966

What about the years with very low Eurasian snow cover (bottom 10) since 1966? 10th lowest to all-time lowest? The 500 mB jet seems consistently stronger in years with lower Eurasian snow cover. The northern Pacific water temperatures seem cooler overall. Only 1975, 83 and 2007 has widespread above normal temperatures in late October and early November.

1997

2007

1974

1983

1980

1979

1981

1975

1982

1988

Comparing high and low Eurasian snow cover to the ENSO state shows a blend to either side--cool and warm. 8 of the 20 years occurred during a strong ENSO state. Overall, there doesn't seem to be an overall trend which suggests that other factors are at play aside from ENSO.